As wireless communication networks have become ubiquitous in many parts of the world, a variety of communications technologies and protocols have been developed and standardized for providing inter-working functionality between communication networks that are based on different technologies. The Third Generation Partnership Project (3GPP) defines cellular telephone technologies such as the Global System for Mobile communications (GSM), Wideband Code Division Multiple Access (WCDMA), the packet-switched based Long Term Evolution (LTE) and the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN). Similarly, 3GPP2 defines cellular telephony technologies, such as CDMA 2000, including a single-carrier Radio Transmission Technology (1xRTT), which supports circuit-switched services and High Rate Packet Data (HRPD). The 3GPP and 3GPP2 bodies further define inter-working functionality between several of these systems.
One such inter-working functionality is the support for Circuit-switched Fall Back (CSFB) to 1xRTT, also known as enhanced CSFB to 1xRTT (e1xCSFB). e1xCSFB is characterized in that an end user equipment (UE) that supports both the LTE and 1xRTT radio interface (although not at the same time) and that camps in LTE may handle any Circuit-switched (CS) call in 1xRTT. This means that the UE switches over, or is handed over by the network, to 1xRTT whenever it is involved in a Mobile Terminated (MT) or Mobile Originated (MO) call.
Such a scenario is exemplified in FIG. 1, which is a simplified illustration of an LTE system 100 interconnected with an 1xRTT system 101, where an 1xCS CSFB enabled UE, hereinafter referred to as UE 102, may access the LTE system 100 via E-UTRAN 103. E-UTRAN 101 is interconnected to the 1xRTT system 101 via a Mobility Management Entity (MME) 104 and an Interworking System (1xCS IWS) 105.
For MT calls it is required that the UE 102 receives a page message from the 1xRTT system 101 in order to make it aware of an incoming call received via 1xRTT Mobile Switching Center (MSC) 104. This page message is sent from the 1xRTT system 101 via the LTE system 100 as a data or signaling message. For such a paging process to work, the UE 102 first needs to register to the 1xRTT system 101 via the LTE system 100. In addition, the e1xCSFB procedure for MT/MO calls also relies on UE 102 signaling to the 1xRTT system 101 to make necessary preparations, such as resource preparations in the 1xRTT system 101, before the UE 102 can switch over to the LTE system 100, wherein this signaling is typically tunneled via the LTE system 100. CSFB is further specified in the 3GPP Technical Specification TS 23.272, “Circuit-switched (CS) fallback in Evolved Packet System (EPS); Stage 2”.
There is, however, no congestion control mechanism defined in e1xCSFB that indicates when the 1xRTT system is overloaded, and consequently there is no support for reducing the load originating from incoming MT/MO call attempts in situations where the 1xRTT is overloaded. For UE accesses performed directly in the 1xRTT system, such functionality may be handled on the basis of persistence parameters (PSIST), which are normally broadcasted via the 1xRTT cells of the 1xRTT system. In such a situation PSIST may be used to inform the UE of information such as whether it is allowed to access an 1 xRTT cell and/or the probability of establishing a connection with the 1xRTT system.
For the internal congestion control to work also for e1xCSFB MT/MO call attempts, a proposal referred to as “Addition of 1xRTT persistent parameters to SIB8” and 3GPP TSG-RAN WG2 Meeting “67bis R2-095645,”CR to 36.331 for 1xRTT persistence parameters in SIB8″ has been presented in 3GPP TSG-RAN WG2 Meeting #67bis R2-095644. In the mentioned proposal it is suggested that 1xRTT persistence parameters are broadcasted also in the LTE broadcast channel. In the mentioned examples the information is broadcasted in System Information Block (SIB) 8. When a network operator detects that there is overload in the 1xRTT system, it will update the PSIST parameters in the LTE system so that the load of incoming e1xCSFB attempts is reduced, or even completely stopped, for a certain time period. The UE will then read the PSIST parameters before attempting to perform the e1Xcsfb and in the event of congestion the attempt will be stopped before the UE performs any signaling for starting the CSFB procedures towards the LTE system.
A significant problem with this solution is that there is no standardized mechanism for making the congestion situation in the 1xRTT system known also in the LTE system. Even though it would be possible for the operator to use some proprietary inter-working/signaling between the Operation and Maintenance (OAM) systems of the LTE and 1xRTT systems to pass the congestion information between the two systems, this alternative has the disadvantage that, due to the absence of standardization, special solutions that may depend on the operators of the two inter-connected systems and the LTE/1xRTT vendors involved will be required.
Furthermore, the congestion can in many cases be of a more-or-less dynamic nature, and may also depend on unforeseen events in the cellular networks or events which are very difficult to predict, such as sports or music performances, which typically may result in a large instantaneous occasional influx of people, traffic accidents or congestions, which may result in an occasional increase in cellular traffic in the cellular networks. Any of these events may result in the OAM systems having to update or trigger an update of the PSIST parameters dynamically. However, OAM systems are normally not designed to handle dynamic functionality, which is normally handled by the traffic functions and via signaling.